Discussion
ERWT in the spine is very rare. ERWT occurring within teratomas (5-10)
is pathologically described as teratoid Wilms tumors and separate
entities from the classic ERWT described in this case report. No
elements of teratoma were found in our patient.
Posalaky et al. (11) described nephrogenic rests in the spine and
suggested that these cells could undergo malignant transformation. There
was no associated spinal dysraphism in their two reported cases, and the
nephrogenic rests identified in the spine were benign with no evidence
of ERWT. However, ten years later, Fahner et al. (12) described ERWT in
the spine without spinal dysraphism.
The association of spinal dysraphism with ERWT is explained by the
embryonic rest hypothesis of cancer development (13). This theory states
that remnants of embryonic tissue occur in adults and children and that
a change in the surrounding tissue would allow the embryonic tissue to
resume proliferation and to produce masses of cells that resemble fetal
tissues (14). Thus, it has been proposed that ERWT arises from
pluripotent (mesenchymal) cell rests that undergo malignant
transformation (13,14). Fernbach et al. (15), citing Grobstein’s (16)
study, suggested that the embryonic central nervous system is capable of
inducing nephrogenic differentiation in the embryonic mesenchyme from
which the spine develops. Furthermore, Deshpande et al. (17) reported an
ERWT within the dorsal lumbar spine’s subcutaneous fat without
associated spinal dysraphism, very similar in location to the
nephrogenic rests described by Horenstein et al. (18), both of which had
no associated spinal dysraphism.
The abortive formation of nephrogenic elements and the location of the
tumor in the bifid spine outside the path of the developing kidneys, as
in our case, supports the hypothesis that mesenchymal rests trapped in
the wrong location and under aberrant stimulation develop into
nephrogenic rests that undergo malignant transformation into ERWT. (13)
In a review of 34 cases of ERWT, Coppes et al. (19) analyzed therapy and
survival. They suggested that all patients with ERWT receive
postoperative chemotherapy, with the same regimen as for a renal Wilms
tumor of the comparable stage. Sastri et al. (20) reviewed three
additional cases and summarized a total of 48 cases of ERWT, and
concurred with the recommendations of Coppes et al. (19). Based on these
recommendations, our patient was treated according to the latest
guidelines for renal Wilms tumor, following the National Wilms Tumor
Study-V regimen for EE4A.